VHP Photo Glossary: Tephra

Photograph by D. Wieprecht

Tephra

Tephra is a general term for fragments of volcanic rock and lava regardless
of size that are blasted into the air by explosions or carried upward by hot
gases in eruption columns or lava fountains. Tephra includes large
dense blocks and bombs, and small light rock debris such as scoria,
pumice, reticulite, and ash.

As tephra falls to the ground with
increasing distance from a volcano, the average size of the individual
rock particles becomes smaller and thickness of the resulting deposit
becomes thinner. Small tephra stays aloft in the eruption cloud for
longer periods of time, which allows wind to blow tiny
particles farther from an erupting volcano.

Photo 1:

Tephra erupted by Mount St. Helens on 18 May 1980 ranging in
size from ash (left 2 piles) to lapilli (right 2 piles).

Photograph by E. Wolfe on 24 June 1991

Photo 2:

Volcanic ash falls to ground and creates darkness,
Mount Pinatubo in the Philippines.